The electoral strategy of the Cameron-Osborne duumvirate, since the start of this Parliament, has been to craft a voter mood of mingled confidence and anxiety for its end – confidence that economic recovery is strong enough to be sustainable under the Conservatives, and anxiety that it isn’t strong enough to be sustainable under Labour (as it was post-1997 for several years). The plan has always been to fight a 1992-style election campaign in which Ed Miliband will be painted as today’s Neil Kinnock. David Cameron was head of Conservative Central Office’s political section during that contest, and is itching to fight it all over again.

At Party Conference last month, the leadership hit the major scales on the piano hard. As Peter Hoskin has pointed out on this site, George Osborne pledged to scale back public spending by another £25 billion near its start, and Cameron himself wrapped the event up by dangling the prospect of tax cuts, a theme he followed up after it ended – a higher personal allowance, cuts in the higher rate of income tax, even (briefly) an inheritance tax cut. The stress was on what the Prime Minister once called “change, optimism and hope”. The structural deficit would be eliminated, tax cuts would come, and living standards, so squeezed and battered since the start of the Great Recession, would rise.

But in today’s article by the Prime Minister in the Guardian, he switches to the minor scales. “Red lights are flashing on the global economy,” its headline cries. The text is full of dire warnings. “The eurozone is teetering on the brink of a possible third recession” and “global trade talks have stalled”. There is an epidemic of Ebola, conflict in the Middle East, illegal action by Russia in Ukraine, “instability and uncertainty”. Cameron points towards some of the Government’s successes: “record numbers of new businesses”; “the largest ever annual fall in unemployment”; “employment up 1.75 million in four years: more than in the rest of the EU put together”.

None the less, there is a problem at the heart of all this. It certainly isn’t a willingness by voters to back Ed Miliband, who is turning out to be not so much Kinnock as Michael Foot: indeed, his ratings are even worse. Rather, it is that the structural deficit is a mammoth in the room. “In recent years,” the Prime Minister writes, “too many politicians offered easy answers, thinking we could spend, borrow and tax our way to prosperity”. The Conservative Manifesto aimed “to eliminate the structural deficit over a Parliament”. The Coalition Agreement said that the Government will “significantly accelerate the reduction of the structural deficit over the course of a Parliament”.

Five years on, the deficit is still coming in at over £100 billion. Not all of it is structural – but the plain fact is that Osborne has not succeeded in fulfilling the ambition which was set out in that manifesto. And now, as Cameron acknowledges, growth elsewhere is slowing. That means fewer opportunities for exporters, which in turn means lower tax receipts for the Treasury and an even higher mountain of deficit reduction to scale. Even Ed Balls concedes that a further spending scaleback is necessary – though his response to the challenge isn’t urgent enough, and he doesn’t have the credibility to deliver it anyway.

The question to all the parties therefore is: where on earth are the cuts going to come from? Earlier this year, the IFS said that “the post-2015 administration [will have] to make the deepest cuts since 1948″ – and that was before much of the slowdown of which the Prime Minister warned. We know that a Conservative Government would continue, as now, to protect the aid and health budgets: the ring-fencing of the latter looks like a declaration of intent to protect the older voters on whose support Cameron and Osborne will depend next May. The health pledge is as essential in political terms (at least insofar as it applies to hospitals) as it is unsustainable in economic ones.

The truth is that too few voices are challenging the easy answers of which the Prime Minister warns. His own, frankly, sounded like one of them during the conference season. His article today could be the start of a necessary corrective, though the location for it makes no sense – since the appeal on the economy he will make next May won’t be pitched to Guardian readers. We need a commission of all parties and none to highlight, dramatise and probe the challenge of health, social services and pensions spending – and give political cover to solutions that government should implement (such as a higher age for receipt of the state pensions and more co-payment in healthcare).

We need a Balanced Budget Plus rule that would requiring budgets to be balanced over each economic cycle – with the Office of Budget Responsibility would be given the right and duty to block any budget that failed to meet this rule. We need a debt ceiling would be defined in law, which public borrowing would not be allowed to exceed. We need a permanent cap on public sector headcount and payrolls to provide a third line of defence against fiscal irresponsibility. In short, we need the kind of framework set out in the ConservativeHome Manifesto for deficit reduction. We cannot afford to go back to the same old discredited cycle of debt, collapse – and more debt.